During the coming year our emphasis will shift from protein-calorie malnutrition to iron deficiency. In particular, we will follow up recent studies that suggest that serum ferritin concentration reflects tissue iron stores. The amount of ferritin in serum (10-200 micro gram/ml is miniscule and is measured by a sensitive radioimmunoassay in less than 0.1 ml of blood. As iron deficiency develops, serum ferritin appears to decrease before serum iron. This is, therefore, an exciting new area of iron metabolism, especially in terms of defining the metabolic role and characteristics of serum ferritin and in its promise for early diagnosis and nutritional screening. We will investigate serum ferritin in relation to other iron compounds during normal development and in iron deficiency in the rat which will include measurements of total brain iron, brain ferritin and brain monoamine oxidase activity in rats placed on iron deficient regimens. Studies in man will await action of the Committee on Human Experimentation which is pending.